Methamphetamine is easily the most popular drug consumed in New Zealand each week, with an estimated $500 million spent on the Class-A drug each year.

New Zealanders spend nearly $1.4 million cash on methamphetamine every single day, according to police analysis of three months of drug testing of wastewater.

Described by scientists as "one large urine test", the wastewater testing started with three sites in 2016 - Whangarei, Auckland's North Shore and Christchurch - but was rolled out nationwide last November.

The ESR testing at 38 sites now captures 80 per cent of the population and officials hope it will paint a clearer picture of New Zealand's drug habits.

An average of 16kg of methamphetamine has been consumed each week in November, December and January according to the preliminary results released today.

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This costs the country an estimated $20 million each week in social harm - or $1 billion a year - said Police Commissioner Mike Bush.

"These early results give us an idea of the potential for this type of data and, as testing continues, it will enhance our understanding of the demand and supply of illicit drugs and the associated harm caused in our communities," Bush said in a press release.

"The long-term results will help police and other agencies make informed decisions around drug treatment services, and initiatives to combat organised crime groups dealing in methamphetamine and other drugs.

"Three months of results, however, are only an early indicator of illicit drug use levels in New Zealand and cannot yet be used to draw any firm conclusions.

"We expect that after twelve months of nationwide testing a robust baseline measure of illicit drug use will be established."

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The preliminary figure of 16kg consumed each week means users would pay $9.6 million each week, or $500m each year.

"The wastewater data suggests that there is a strong market across New Zealand for methamphetamine, with it being found in all communities tested and found on every single day of testing," Detective Superintendent Greg Williams wrote in an affidavit.

His affidavit was given as expert evidence in a recent hearing at the Court of Appeal which could lead to a major shakeup of prison sentences for methamphetamine crimes.

Williams said the data suggested methamphetamine was regularly consumed as a daily habit, while testing showed more cocaine or Ecstasy was taken in the weekend, indicating recreational use.

In Auckland alone, 8kg of the methamphetamine was detected each week over the three-month period.

From this, Williams estimated the annual total to be 416kg a year, or $197 million in cash - $550,000 a day - at the $500 gram price.

The first results of the national wastewater testing show Northland consumes the most meth on a per capita basis. Photo / Police.
The first results of the national wastewater testing show Northland consumes the most meth on a per capita basis. Photo / Police.

The data for the established sites in Christchurch and Whangarei stretch back several years.

Across the course of a year, ESR found that on average in Christchurch 87g of meth was consumed every day.

Based on retail value of $600 per gram in Christchurch at the relevant time, Williams said the meth dealers were receiving $52,200 cash every a day, or $19m over the year.

Detective Superintendent Greg Williams, head of the National Organised Crime Group. Photo / Mike Scott.
Detective Superintendent Greg Williams, head of the National Organised Crime Group. Photo / Mike Scott.

However, the data from the original three sites proved a belief by police that methamphetamine was more prevalent in Northland.

"Comments such as 'it's snowing in Northland', meaning there was lots of Ice or methamphetamine, were common," Detective Senior Sergeant Mike Varnam wrote in his affidavit to the Court of Appeal.

Varnam helped set up the Te Ara Oranga programme in Northland, a joint initiative between the Northland DHB and police to help steer meth users towards treatment, not court.

The wastewater testing illustrated the "disproportionate" drug use in Whangarei when compared to Auckland and Christchurch on a population basis.

The most recent Ministry of Health drug survey in 2015 showed around 0.9 per cent of the New Zealand population consumed methamphetamine, down from 2.2 per cent in 1997.

But the police say wastewater testing helps build a "true picture" as surveys rely on the willingness and accuracy of those being questioned.

Wastewater testing shows methamphetamine consumption has increased since 2016, said Detective Sergeant Daniel Lyons from the National Drug Intelligence Bureau, a joint team with Customs and the Ministry of Health.

The project also helped gives an international perspective on New Zealand's problem, as wastewater is also monitored for drug use in Australia, Portugal, Belgium, Germany and Norway.

The data from the pilot in North Shore, Christchurch and Whangarei shows New Zealand sample locations were higher than cities in Europe (on a per 1000 person basis) but lower than Australia.

MDMA was the second most popular drug in New Zealand, with around 4kg consumed each week, while less than 700g of cocaine was consumed each week.